What are Core Web Vitals?
Core Web Vitals is a set of standardized metrics that are measured and together indicate the overall user experience on a website. There are primarily three parameters being measured: page loading performance, how interaction on the website works, and the page’s visual stability. When user experience is broken down into three concrete Core Web Vitals, it becomes easier for you as a website owner to identify and optimize pages that score poorly on one or more of these parameters.
Page loading of visible elements - Largest Contentful Paint
Users have little patience, so it is crucial that the most important elements on a website load almost instantly. This is captured in the metric known in English as LCP. Largest Contentful Paint measures the time from when a user lands on the page until the largest content block on the page has loaded and is visible to the user. This applies to the part of the page that is visible in the viewport before the user scrolls down. What is typically measured is a header image, a text block, or a video. To achieve a strong assessment from Google, LCP should be a maximum of 2.5 seconds.
The time from user action to page response - First Input Delay
First Input Delay (FID) measures how long it takes for an element on the page to respond to a user action. For example, the time from when the user clicks a “show more” button until the expanded text appears. The goal of FID is to encourage developers to reduce the time users have to wait for the browser to respond to their interactions. A short response time makes on-page interactions more efficient. Ideally, FID should be under 100 milliseconds.
How elements on the page move while the page is loading - Cumulative Layout Shift
The layout and design of the page have a major impact on the overall user experience. On some websites, visual elements on the page move around while the page is loading. This is called Cumulative Layout Shift (CLS), and CLS measures how often this happens on a webpage. For example, it can mean that a button shifts position while the page is loading, which can be very frustrating for the user. The goal is therefore to keep this to an absolute minimum.
Summary
Core Web Vitals are metrics that Google uses to clarify what they mean by good user experience. Of course, there are several other things being measured, but these have been identified as important factors that are both very concrete and put the user at the center. This is important because it shows what users actually encounter on the website.
